The present invention relates generally to liquid crystal displays, and more particularly, to systems for backlighting liquid crystal displays.
The principal of operation of liquid crystal displays (LCDs) is well known in the art, but for purposes of understanding the present invention, it can be stated that LCDs operate by reducing the transmissibility of light through a thin layer of liquid crystalline (LC) material when an electric field is applied. Because LCDs are not self-illuminating, backlighting of the LC matrix is required for an LCD to be viewed. Typically, backlighting is accomplished with one or more fluorescent lamps or lamp sections located in a luminaire cavity behind the LC matrix. A diffuser is also typically located between the LC matrix and the lamp sections in order to blend the light and/or to facilitate viewing of the LCD from a variety of angles.
Current backlighting systems introduce a number of luminance related problems. For example, LCDs using current backlighting systems suffer from non-uniformity in the region near the edge of the display. Edge, surfaces, typically the LCD frame, tend to scatter and/or absorb luminance energy. This creates a dark region or area of low luminance near the edge of the display. As the viewing angle increases, the luminance decrease near the edges of the display becomes more significant. In some applications such as in avionics displays, this "edge effect" or "luminance roll-off" is unacceptable. Low mean luminance of the display is another related problem with existing LCDs.
Frequently, manufacturers of LCD backlighting systems move the lamps back from the LC matrix and the diffuser in order to blend the luminous flux coming off of the lamps so that viewers cannot see the contour of the lamp. However, increasing this distance further exasperates the above described luminance problems. Consequently, a need exists for an improved LCD backlighting system which eliminates or minimizes luminance related problems such as luminance roll-off, low mean luminance and poor luminance uniformity. The present invention discloses a variety of embodiments of such an LCD backlighting system.